In completing wells in poorly consolidated or unconsolidated formations, consideration must be given to sand problems likely to arise during the operation of the well. The incompetent nature of this type of formation requires that a well completion technique include means for excluding sand production. Erosion and plugging effects of sand entrained in produced fluids are well known and if not arrested can seriously reduce well productivity.
The propensity of a formation to produce sand is particularly acute in formations characterized as unconsolidated or poorly consolidated. These terms, as applied to subterranean sedimentary deposits, define a particular class of sedimentary rock, the distinguishing characteristics of which is the absence of a rock matrix made up of sand grains bound into a cohesive mass.
When completing wells in an unconsolidated or poorly consolidated formation, success of in-casing gravel packs using a slotted liner in a perforated casing is highly dependent on established gravel/formation fine size relationships. With study and experience, it is possible to select the proper gravel size to optimize productivity while controlling formation fines invasion into the wellbore. Success of the gravel pack is very dependent on effective placement of the gravel. Ordinarily, this can be successfully accomplished in a vertical wellbore.
Most loosely consolidated formations where fines production is likely to occur are located offshore where many wells are drilled from a single platform. Most wells are drilled on an incline, resulting in completions through the pay intervals at an angle. In these wells, it is more difficult to place a gravel pack effectively due to the inclination of the hole. Because of the inclination of inclined or deviated wellbores, conventional gravel packing procedures meet with limited success in these wells.
As mentioned in industry literature (SPE 24842 "Completion Techniques Used in Horizontal Wells Drilled in Shallow Gas Sands in the Gulf of Mexico" by C. W. Pardo and A. N. Patricks, Texaco, Inc., presented at the 67 th Annual Technical Conference and Exhibition of the SPE in Washington, D.C., Oct. 4-7, 1992), horizontal well completions in horizontal, loosely consolidated wellbores is difficult. In this presentation, it was proposed to use pre-packed screens in slotted liners to minimize sand production. As proposed, this technique is limited in that the pre-packed screens are of rigid construction and the materials in the pre-packs are highly susceptible to damage by acids used for stimulating sandstone formations.
Therefore, what is needed is a method for a horizontal well completion whereby a horizontal wellbore in a loosely consolidated or unconsolidated formation is completed with a slotted liner which minimizes wellbore collapse and a flexible sand control device that facilitates positioning while minimizing sand production.